Molecular mechanism of estrogen action to inhibit obesity

雌激素不仅对女性生殖器官有多种作用，而且对包括脂肪组织在内的非生殖器官也有多种作用。雌激素抑制啮齿动物卵巢切除引起的肥胖。我们研究了这种雌激素依赖性抑制肥胖的机制。雌激素显著降低了稳定表达雌激素受体（ER）的基因操纵的3T3-L1脂肪细胞中脂肪积累和脂蛋白脂肪酶（LPL） mRNA以及甘油三酯积累的数量。研究了雌激素对小鼠LPL基因的转录调控作用。将pLPL (1980)-CAT构建体与ER表达载体一起引入分化的3T3-L1细胞。测定CAT活性。内质网主要依赖于配体，对LPL启动子活性的抑制作用是其7倍。我们利用pLPL-CAT报告基因的一组5'缺失突变体，在LPL启动子中寻找雌激素反应性抑制元件。虽然没有经典的雌激素反应元件，但研究表明，位于（-1856/-1850）的ap -1样TGGAATTC序列负责雌激素对LPL基因转录的抑制。用TGAATTC序列探测的电泳迁移率转移试验证明了特定dna -核蛋白复合物的形成。有趣的是，该复合物不受添加任何针对ER、c-Jun、c-Fos、JunB或JunD的抗体的影响。这些结果可能表明，除了经典的ERE和结合蛋白之外，存在一种独特的信号通路，利用独特的雌激素反应元件可能调节LPL基因的转录。

Estrogen exerts a variety of effects not only on female reproductive organs but also on nonreproductive organs, including adipose tissue. Estrogen inhibits obesity trggered by ovariectomy in rodents. We studied the mechanism underlying this estrogen-dependent inhibition of obesity. Estrogen markedly decreased the amounts of fat accumulation and lipoprotein lipase (LPL) mRNA as well as triglyceride accumulation in genetically manipulated 3T3-L1 adipocytes stably expressing the estrogen receptor (ER). Transcriptional regulation of the murine LPL gene by estrogen was then studied. A pLPL (1980)-CAT construct, along with an ER expression vector, was introduced into differentated 3T3-L1 cells. and CAT activities were determined. ER, mostly ligand-dependently, inhibited the basal LPL promoter activity by 7-fold. We searched the LPL promoter for an estrogen-responsive suppressive element by employing a set of 5'-deletion mutants of the pLPL-CAT reporter. Although there was no classical estrogen response element, it was demonstrated that an AP-1-like TGGAATTC sequence located at (-1856/-1850) was responsible for the suppression of the LPL gene transcription by estrogen. An electrophoretic mobility shift assay probed with the TGAATTC sequence demonstrated formation of a specific DNA-nuclear protein complex. Interestingly, this complex was not affected by the addition of any antibodies against ER, c-Jun, c-Fos, JunB, or JunD. These results may indicate the existence of a unique signaling pathway utilizing a unique estrogen response element other than classical ERE and binding proteins which possibly regulate transcription of the LPL gene.